Donkey: hero or villain of the parasite world? Past, present and future

This collection of articles provides an account of five presentations delivered at the 19th International Conference of the World Association for the Advancement of Veterinary Parasitology(WAAVP) (held in New Orleans, Louisiana, USA, from 10 to 14 August 2003) in a symposium session on Donkey parasites, organised by Andrew Trawford and Catherine Morriss and moderated by Dr. Elisabeth Svendsen. The focus was on the role of the donkey in the advancement of parasitology, diagnosis and identification, methods of control and anthelmintic resistance.

Cysticercosis in the pig

Taenia solium cysticercosis is still an important parasitosis in rural pigs in many developing countries, México among them. The main causes for the persistence of this condition are lack of hygiene in the rural communities, lack of education of the animal owners, lack of control in the trade of pigs and their meat and lack of conscientious meat inspection. The pig production systems in the marginated areas of Mexico are briefly mentioned and it is stressed that among the important reasons for the persistence of the reproductive cycle of Taenia solium is the fact that appropriate toilet facilities in village dwellings are not mandatory. The diagnostic methods of cysticercosis in the living pigs and in their meat are discussed and the degenerative stages of the larvae as well as methods to test their viability are explained. The treatment of infected pigs and their meat is discussed. Recommendations for control programmes are given.

Impact of naturally acquired Taenia solium cysticercosis on the hormonal levels of free ranging boars

In chronically infected BALBc/AnN male mice, Taenia crassiceps cysticercosis induces changes in the host's sex steroids hormone that lead to their estrogenization and deandrogenization, with possible repercussions on their susceptibility to infections. Here reported are the serum steroid levels in free range cysticercotic male boars. Therefore, the possible effects of Taenia solium cysticerci over the pig steroid levels were evaluated. Herein are described the sex steroids and cortisol levels of non-cysticercotic (n=25) and cysticercotic (n=22) adult boars, as diagnosed by tongue inspection, all free-ranging in a typical village of an endemic rural area in Mexico. A significant reduction of testosterone (P=0.022) and a likely one of 17beta-estradiol (P=0.08) levels were found in the cysticercotic boars in comparison with those non-cysticercotic, whilst no significant differences in the cortisol and DHEA levels were detected. Serum levels of specific antibodies did not correlate with infection nor with the levels of any of the hormones measured. Results suggest that T. solium cysticercosis significantly affects the hormonal status of its porcine host independently of their antibody response.

Molecular identification of Echinococcus granulosus genotypes (G1 and G7) isolated from pigs in Mexico

With the aim of genotyping Echinococcus granulosus cysts found in Mexican livestock, we collected hydatid cysts from the livers and lungs of pigs in slaughterhouses in the state of Morelos, Central Region of Mexico. DNA was extracted from the parasites and examined by polymerase chain reaction (PCR) of rDNA internal transcribed spacer 1 (ITS1-PCR), Eg9-PCR, Eg16-PCR, and PCR-restriction fragment length polymorphism (PCR-RFLP). In addition, fragments of the genes coding for mitochondrial cytochrome c oxidase subunit 1 (CO1) and NADH dehydrogenase 1 (ND1) were sequenced. Two different genotypes of E. granulosus were unequivocally identified, the common sheep genotype, G1, and the common pig genotype, G7. The G1 genotype of E. granulosus has not been previously demonstrated in Mexico. Because of its recognized infectivity in humans, G1 genotype is a direct threat to human health and its presence in Mexico is consequently of immediate public health importance and epidemiological relevance.

Study of the genetic origin of the Mexican creole donkey (Equus asinus) by means of the analysis of the D-loop region of mitochondrial DNA

The aim of this work was to analyse the genetic origin of the Mexican Creole donkey, as well as its genetic diversity, by comparison with Spanish and African donkey populations by means of the D-loop region of mitochondrial DNA. To this end, the genomic DNA of 68 Mexican Creole donkeys from eight geographical regions in six States of the Republic of Mexico and from a Sicilian donkey was obtained. By the polymerase chain-reaction technique (PCR) a fragment of 541 bp was amplified, corresponding to the most informative region of the mitochondrial DNA, the D-loop. The fragments were subsequently sequenced. The analysed sequences revealed 10 new Mexican haplotypes that were different from those of the Spanish and African breeds with which they were compared, showing high levels of genetic diversity. Analysis of the phylogenetic relationships in the different Creole varieties showed a tendency of origin towards Spanish breeds, mainly the Andaluza, Zamorano-Leonesa and Majorera from the Canary Islands; these in turn showed an African origin, seven Mexican haplotypes and three haplotypes similar to those analysed by Aranguren and colleagues (2004) of Spanish and African breeds being obtained. This work allows us to reach the preliminary conclusion that the origin of Mexican Creole donkey populations in the different states of the Republic of Mexico is clearly of Iberian origin, the Spanish donkey breed Andaluza being the main one contributing to the populations of the Mexican Creole donkeys, followed by the Spanish breeds Zamorano-Leonesa and Majorera from the Canary Islands, and that the populations possess high levels of genetic diversity.

Live Weight Estimation of Donkeys in Central México from Measurement of Thoracic Circumference

Body measurements (length from nape of neck to the withers; height to withers; length from withers to tail root; length from shoulder to tuber ischii; thoracic circumference; umbilical circumference) were taken and correlated with live weight from 160 donkeys (mean +/- standard deviation = 6 +/- 2.6 years old) in Central Mexico. The age was assessed from dentition. Sex of the donkeys was also recorded. Sex was an important factor of variation (p = 0.011). Live weight was estimated using two allometric models. Model 1: Live weight = beta x (thoracic circumference)beta1. Model 2: Live weight = betao x (height to the withers) beta1 x (thoracic circumference) beta2. Separate prediction equations were produced for males and females, plus one for the total sampled. The 'best fit' models, were those using thoracic circumference to predict the live weight. Males: live weight = 0.018576 x (thoracic circumference)1.84107 (R2 = 0.9839). Females: live weight = 0.031255 x (thoracic circumference)1.72888 (R2 = 0.9839). The equations derived to estimate the live weight of donkeys in Britain, Morocco and Zimbabwe were less satisfactory for use with donkeys from Central Mexico because they overestimated the live weight.

Synthetic peptide vaccine against Taenia solium pig cysticercosis: successful vaccination in a controlled field trial in rural Mexico

Taenia solium cysticercosis seriously affects human health when localised in the central nervous system (CNS) and causes great economic loss in pig husbandry in rural areas of endemic countries. Increasing the resistance to the parasite in the obligatory host pig may help in curbing transmission. Three synthetic peptides based on protein sequences of the murine parasite Taenia crassiceps, which had previously been shown to induce protection in mice against homologous challenge, were tested as a vaccine against T. solium cysticercosis in pigs. Vaccinated and unvaccinated piglets (240 in all) were distributed in pairs among the peasants' households of two rural villages in Mexico in which 14% of the native pigs were cysticercotic. Ten to twelve months later, the effect of vaccination was evaluated at necropsy. Vaccination decreased the total number of T. solium cysticerci (98.7%) and reduced the prevalence (52.6%). The natural challenge conditions used in this field trial strengthen the likelihood of successful transmission control to both pig and human through a large-scale pig vaccination program. We believe this is a major contribution in anticysticercosis vaccine development as these rather simple yet protective peptides are potentially more cost-effective to produce and less variable in results than antigens that are more complex.

Failure to incriminate domestic flies (Diptera: Muscidae) as mechanical vectors of Taenia eggs (Cyclophyllidea: Taeniidae) in rural Mexico

Flies caught in homes in a rural village in Guerrero, Mexico, between November 1994 and August 1995 were assessed for their role in the transmission of Taenia solium L. Most (99%) of the trapped flies were Musca domestica L. None of the 1,187 guts or 1,080 legs of the flies contained T. solium eggs. Pigs roam freely in this village consuming human fecal material immediately after defecation, thereby limiting fly contact with T. solium eggs.

Vaccination against Taenia solium cysticercosis in underfed rustic pigs of México: roles of age, genetic background and antibody response

Vaccination of pigs of mixed genetic make-up, raised as rustically as done in rural Mexico, resulted in effective protection to experimental challenge against Taenia solium cysticercosis. Maximum protection was achieved if pigs were immunized at 70 days of age. There was large variation of viable parasite load within vaccinated pigs and controls, which is suggestive of significant genetic factors influencing susceptibility, besides immunization. Our results strengthen the advisability of pig vaccination for control of T. solium cysticercosis, since it lowers the number of viable cysticerci capable of transforming into tapeworms.

Taenia solium cysticercosis: immunity in pigs induced by primary infection

The present study demonstrates that pigs experimentally infected with Taenia solium eggs develop resistance to reinfection that lasts at least five months. Thirteen 2-month-old piglets were infected with eggs of Taenia solium. After 5 months, two pigs were euthanized and five were challenged with eggs from a second tapeworm. Nine months after the first infection, six pigs were challenged with a third tapeworm. All 11 challenged pigs were euthanized 2 months after reinfection. In order to confirm the infectivity of the eggs, several piglets were inoculated with each taenia. Two of the five pigs reinfected after 5 months did not develop metacestodes, two showed few caseous non-infective forms and in the fifth pig, 14% of the metacestodes were vesicular and 86% colloidal and caseous. In the six animals challenged 9 months after the first infection, three were heavily infected with vesicular metacestodes and the other three showed only colloid and caseous forms in muscles. All parasites found in brains were vesicular. We conclude that immunity due to primary infection lasts at least 5 months. At 2 months of infection antigens of 24 and 39-42 kDa were the most frequently recognised. In those pigs with only a few caseous cysts in muscles and/or vesicular ones in brains no antibodies were detected.

Limitations of current diagnostic procedures for the diagnosis of Taenia solium cysticercosis in rural pigs

The aim of the present study was to evaluate diagnostic procedures for porcine cysticercosis. Sera were obtained from 32 pigs reared in commercial farms, 47 pigs before and after experimental infection, 42 carefully necropsied rural pigs and 191 slaughtered pigs from rural communities in which the presence of the Taenia solium metacestode was assessed by tongue dissection. Sera were analyzed by ELISA to detect antibodies against T. solium antigens and to detect parasite antigens. Most sera from the necropsied rural pigs were also evaluated by the Western blot method. Antigen and antibody ELISA detection assays showed high sensitivity and specificity when applied to sera from pigs reared in commercial farms. In contrast, all methods (Ag-ELISA, Ab-ELISA assays, EITB and tongue inspection) showed lower sensitivity and specificity when applied to the generally lightly infected rurally reared pigs. The probability distribution of cysts in carcasses were also determined. These results emphasize the difficulties in detecting cysticercosis in rural pigs with low levels of cyst burdens.

Diagnosis of porcine cysticercosis: a comparative study of serological tests for detection of circulating antibody and viable parasites

Epidemiological studies of porcine cysticercosis require identification of pigs harbouring viable Taenia solium cysticerci and estimates of the degree of exposure to the parasite in the pig population destined for human consumption. Identification of infected pigs with viable larvae is achieved through detection of their secretory products. However, detectable levels of circulating antibody may also be present in the absence of viable larvae. In this study, both types of tests have been evaluated in groups of pigs experimentally infected with T. solium. Detection of viable cysticerci was achieved using a monoclonal antibody-based (HP10) antigen capture assay. HP10 epitope-bearing antigens have now been demonstrated in T. solium and T. crassiceps cyst fluid and excretion/secretions. Serum antibodies were measured in ELISA assays using two parasite preparations as antigens; T. solium cyst fluid and T. crassiceps cyst fluid antigens bearing the HP10 epitope. Low-background values were obtained with sera from non-infected animals in all the assays used. In heavily infected pigs, both antigens and antibodies were detected at least 29 days and up to 200 days post-infection (pi), while in lightly infected pigs antigen and antibodies were first observed between 61-97 days pi. Thus, the levels of the serum antigen and antibody varied with the intensity of the infection.

Taenia solium cysticercosis in young pigs: age at first infection and histological characteristics

In spite of the vast knowledge that exists in the fields of immunology, biochemistry, diagnosis and treatment, the basic facts about the dynamics of the transmission of Taenia solium are incomplete. The present study determines the age at which piglets become infected in a rural community of Mexico, where the climate is divided into the dry and rainy seasons. It was found that piglets become infected during the dry months, not so during the rainy season. They pick up eggs at the age of 2 to 4 weeks and the metacestodes are present in the liver. In older animals aged 4 to 6 months, the larvae were also found in the muscles. In a 6-month-old pig larvae were found in the muscles and brain. These findings may be explained by behavioural studies of free living pigs and climatic conditions.

Experimental Taenia solium cysticercosis in pigs: characteristics of the infection and antibody response

Pigs were infected with taeniid eggs to study the susceptibility to infection and reinfection of the animals of mixed breeds and of different ages, the viability and death of the metacestodes in the host tissue, and the antibody response which accompanies these events. Sixteen pigs were infected with Taenia solium eggs for this purpose. At necropsy metacestodes were counted in 2 kg of shoulder muscles and classified as vesicular or caseous, and all the metacestodes in brains were counted and classified. The results show that pigs inoculated at 49 and 60 days of age became infected to different degrees and reacted differently to the presence of parasites. In the brain the metacestodes remain viable for longer periods than in muscles. Enzyme-linked immunosorbent assay (ELISA) showed a significant rise in antibodies after infection, which started to decrease 92 days post-infection (p.i.). Pigs with viable cysts remained seropositive up to the end of the experiment (281 days p.i.). Antibody levels rose further after reinfection or after treatment. The results of Western blot were comparable to those of ELISA. Antigens of 13, 14 and 18 kDa were most frequently recognized in early infections and then started to decrease 92 days p.i., while the antigens of 42, 50 and 24 kDa were recognized during later stages of infection (200 days p.i.). The results suggest that older animals are more resistant to the infection [corrected].

Histological description of tomographic images of Taenia solium cysticerci in pig brains

In the computed tomography (CT) scans of five pigs with neurocysticercosis (Taenia solium), interesting lesions produced by the larvae were selected. The pigs were euthanized and the corresponding lesions in their brains identified and processed for histopathology. It was found that the hypodense areas in CT scans corresponded to vesicular larvae that are presumably viable. The hyperdense areas were either solid in nature or had formed a rim around a hypodense center and in the brain slice they were either solid granulomas or colloidal cysts with inflammatory reaction in the periphery, perivascular cuffing, and vasculitis. It was not always possible to classify larvae as meningeal or parenchymatous in the CT.